This invention relates to magnetic head assemblies applicable to magnetic disk drive systems. More particularly this invention relates to high data rate, high efficiency, inductive, thin film heads.
Magnetic transducers (read-write heads) are used for reading and writing magnetically coded data stored on a magnetic storage medium such as a magnetic tape or magnetic disk. In a disk drive system 8, as seen in FIG. 1, a magnetic read-write head 10 is attached to an actuator 12 that flies above a rotating magnetic disk 14. A voice coil motor (VCM) 16 pivots the actuator to position the head 10 over selected circular tracks on the disk 14. The actuator rides on an air-bearing surface over the rotating disk. The disk 14 is attached to a spindle 18 that is rotated by a spindle motor. The disk 14 comprises a substrate having a plurality of thin films deposited thereon. The thin films include ferromagnetic material that is used to record the magnetic transitions, written by the magnetic transducer 10, in which information is encoded. A tape based storage system uses a magnetic transducer in essentially the same way as a disk drive with the moving tape being used in place of a rotating disk.
The magnetic transducer is composed of elements that perform the tasks of writing magnetic transitions and reading the magnetic transitions. In that way, the magnetic transducer is composed of a write-head and a read-head. The electrical signals to and from the read and write heads travel along conductive paths, which are attached to or embedded in the actuator.
A thin film recording head (write head) includes first and second pole pieces that are magnetically coupled together at the xe2x80x9cpole tip regionxe2x80x9d and the xe2x80x9cback gapxe2x80x9d. In the pole tip region, the first and second pole pieces provide first and second pole tips. The pole pieces are typically fabricated using plating techniques. A thin insulative, nonmagnetic gap layer separates the pole tips. The pole tip region is defined by a head surface in what is referred to as the xe2x80x9czero throat heightxe2x80x9d between the air bearing surface (ABS) and the back gap. A yoke, or body portion of the head lies between zero throat height and the back gap. The term back gap is used in the art to mean the back of the yoke. Historically, there was a gap in the back of the yoke and the term back gap continues to be used even though the back of the yoke is now continuous. The back gap is also, more accurately, referred to as the xe2x80x9cback flux closure.xe2x80x9d The body portion of the head contains one or more layers of pancake coils and plurality of insulation layers. The pancake coils couple flux into the pole pieces and/or receive flux there from. Each layer of the head is applied using photolithographic techniques such as photo-resist exposure systems.
There is a continuing strong felt need to increase the data storage density in magnetic storage media. Most efforts to increase magnetic storage density involve techniques for increasing the aerial bit density of the magnetic medium.
In rotating magnetic disk drive systems, the aerial density is the product of the number of flux reversals per millimeter along a data track and the number of tracks available per millimeter of disk radius. Thus, a high aerial data storage density requires recording heads with high linear resolution and a narrow track well.
The thickness of the gap layer at the head""s air-bearing surface determines the linear density of the head, namely how many bits per linear unit length along a data track of a magnetic medium the head can write. The width of the second pole tip determines head track width. The head track width establishes how many data tracks across the width of a magnetic medium per unit length the head can write. The product of these two factors is aerial density.
One way to increase the data rate of a head is to decrease the pitch of the coil layer. The pitch is the distance across one turn of the coil plus one space between the turn and the next turn. It would be desirable for the coil to have a pitch of 1 micrometer (um) or less. Unfortunately, when the data rate is increased with a low pitch coil, the head suffers from an increase in heat and an increase in eddy currents between the first and second pole pieces. Eddy currents reduce the write current, which in turn reduces the write signal across the write gap. One way to reduce eddy currents in the write head is to employ two coil layers which are stacked one above the other, which allows for a shorter write head. However, when designing a head with two layers of coils certain extra steps need to be taken in order to minimize increased sensitivities inherent in such a structure. For example, there is an increased need to planarize and protect the coil layers.
Inductive heads, especially the ones having very high recording densities, have to use full planarization techniques when manufacturing the thin film layers in order to obtain maximum efficiency from the imaging systems used to produce the heads. Independent of the photo-resist exposure system used in the fabrication of the critical photo-resist layers, each layer needs to have a reproducible photo-resist coating thickness as well as a very tight focal plane (which means a small total indicated run-out). Such basic requirements are in order to produce a tight control and resolution. Two of the most critical structures for effectiveness of the inductive head are the magnetic pole (which defines the track width available for the magnetic recording media) and the inductive coil system. While the poles control the aerial recording densities, the size and shape of the coils, together with the basic head design, control the efficiency and speed of the recording head.
There is a need for a head design and a method to produce such a head, which produces a high-density, high data rate head with high magnetic recording efficiency. Such a design can be used with heads designed having a pedestal to improve efficiency as disclosed in commonly owned U.S. Pat. No. 6,259,583, hereby incorporated by reference.
Inductive head designs need to use planarization techniques in order to produce high-resolution coils and poles. The pole fabrication process does not face planarization issues since the pole piece is an isolated structure. However, there are basic problems that arise in planarizing the coils since the coils comprise a plurality of metalized lines.
FIG. 2 illustrates an example of the problems that arise in providing planarization of the already formed coil structure during the manufacturing of a readwrite head. The read portion of the head 20 comprises a first shield (S1) 21, insulation layers 23 that surround a sensor element 22, and a second shield (S2) 24. In the merged head that is shown, the second shield also serves as a first pole piece (P1) 24 (referred to as S2/P1). A coil 26 is deposited on a layer of Al2O3, referred to as alumina (or sapphire) 28, which is used to insulate the coil from P1. The coil comprises a plurality of loops or turns 29 of conductive material (such as copper) with voids 30 in between the loops. Referring to FIG. 2b, the next step in the manufacturing process is the fabrication of the pedestal 31 (when used) and back flux closure (back gap) 32 using NiFe (or other ferromagnetic material) atop the S2/P124 after etching the alumina layer 28.
As shown in FIG. 2c, prior art head designs use alumina (Al2O3) 34 as the filler for the coils 26. Alumina is preferred because it provides good thermal conductivity as well as structural rigidity. Alumina also provides minimum protrusion and has a small expansion coefficient. However, the preferred high data rate head designs call for a very small separation for the high-resolution coil metal loops. For 1-micrometer pitch coils, the separation between loops can be as small as 0.2 micrometers. For such coils where the filler had been just alumina, the alumina sputtering system is incapable of completely filling the voids between the loops and instead, produces smaller voids 35 between the loops. Such voids are unwanted because it delays the thermal dissipation of working heat from the coils. Also, in multi-layer coil system heads (which provide an advantageous high density capability), there is a poor bonding ability between the coil layers in the presence of such voids.
The aspect ratio of the coils, the width versus thickness, is preferred very aggressive to accommodate as many turns per unit area as possible. That reduction of footprint enables the increase of efficiency as well as the reduction of inductance needed to produce a nominal recorded bit in a high coercivity medium.
There is a need for a method of fabricating coils having a coil pitch of 1 micrometer, where the separation of the metal coils is 0.2 micrometers, while the thickness of the metal coils is 2 micrometers. Due to the 10 to 1 aspect ratio between the loops, it is impossible to sufficiently fill the gaps between the loops by known prior art alumina deposit techniques.
An alternate method of manufacturing the coil structure is shown in FIGS. 3a through 3c. The copper coils 26 are fabricated on the alumina layer 28 atop the S2/P124. Next, a hard baked photo-resist material 38 is applied to the coils (FIG. 3b). The pedestal 31 and back gap 32 are fabricated (from NiFe) on top of the S2/P1. Referring to FIG. 3c, more hard-baked photo-resist material 82 is deposited over the coils, and between the coils and back gap, at a thickness of 1.0 micrometer. Applying a hard baked photo-resist material accomplishes the sealing of the voids. The span of the S2/P1 from the first coil loop to the pedestal can be left open and later filled with alumina, since the aspect ratio between the first coil loop and pedestal is not as aggressive as the distance between the loops (the distance from the first coil loop to the pedestal being 4 um). However, if this were all that was done to fill the voids, there would be problems that arise during subsequent manufacturing processes.
It is very difficult for the chemical mechanical polishing (CMP) step, which is used to planarize the head, to planarize the hard-baked photo-resist material while missing the coils by stopping in the hard baked photo resist. Problems in the head arise if the CMP process exposes the copper coils and all of the other materials that are present. More particularly, the CMP process that planarizes the coil structure leaves small recesses along the copper/resist interface. Such recesses are in the order of 0.1 to 0.15 micrometers in depth and width, and are located at the copper side of the interface. It is believed that the amines present in the photo-resist material modify the copper material making it more prone to be etched and eroded. For very high-resolution coils, the voids prove to be almost as wide as the separation between the metal loops. If the quality of the subsequent planarization process is not of significant importance to the head design, simply using a hard baked photo-resist material to cover the coils can be used. However, for high performance heads, as previously described, the planarization of the coil structure is very important.
Alternatively, the coils can be plated very thinly (1.2 micrometers) with alumina wherein the CMP process exposes only alumina and NiFe (or metal of choice for the pedestal and pole piece). However, this process also results in coil resistance and plating uniformity problems.
Therefore, there is a need to be able to fill the voids between the coils and be able to planarize the coil without producing any voids or gaps.
There is a need for a method of planarizing the coils which can be done efficiently and without producing any voids and which would also enable proper insulation for placement of the second layer of coils.
More particularly, there is a need for an efficient and consistent way of planarizing the coil structure in a high efficiency thin film head so that there is proper insulation between the layers of coils even if there are imperfections such as minor grooving or defects on the first layer of coils.
One or more of the foregoing problems are solved and one or more of the foregoing needs are filled by the invention described herein.
It is an object of the preferred embodiment of the invention to provide a planarized coil formation without any gaps or voids, or wherein any minor gaps or voids do not effect a second layer of coils.
It is a further object of the invention to provide a method for planarizing the coils without defects. The absence of the defects permits the further fabrication of other structures on top of the coils without electrical problems such as shorting or optical problems during a subsequent photo exposure reflective notching process.
A thin film inductive head design is provided wherein the head has bi-layer coils, a pedestal and a stitched yoke where the first layer of coils that are on the same plane as the pedestal are filled with hard baked photo resist. The top of the photo resist is removed via an O2 reactive ion etching (RIE) step to reduce its thickness in relation to the adjacent pedestal and coils. The resulting voids are filled with alumina or a hard carbon. A subsequent chemical mechanical (CMP) polishing process is used to planarize the exposed material (Cu, NiFe, and alumina).
A method is provided for manufacturing a thin film inductive write head. A pedestal and back flux closure of ferromagnetic material are formed on opposite ends of a planarized first pole piece. A plurality of coils of conductive material are deposited on top of a layer of alumina deposited on top of the first pole piece between the pedestal and back flux closure. The coils comprise a plurality of loops or turns having voids between the coil loops. A hard-baked photo resist material is deposited in the voids between the coils and the back flux closure. A layer of alumina is deposited over the coils and hard baked photo resist material. The pedestal, back gap, coils, photo resist, and alumina are planarized using a chemical mechanical polishing (CMP) process. The thickness of the photo resist material relative to the coils is reduced using an O2 reactive ion etching process. A hard carbon filler is applied to fill the gaps between the coils and the photo resist material. A CMP process is performed to planarize the carbon filler, coils, back flux closure and the pedestal.
To complete the fabrication of the head, a write gap and track width defining pole are fabricated. For a dual layer coil head design, the second layer of copper coils are fabricated and planarized in the same fashion exposing, after the CMP, the tops of the NiFe poles, alumina, hard carbon or alumina filler, and copper coils. The coils are then insulated from the subsequent ferromagnetic yokes and the ferromagnetic yokes are fabricated.
In the preferred embodiment the coil pitch is 1 um and the separation of the metal coils is 0.2 um and the thickness of the metal coils is 2 um.